Scanners can transform plane photos, pictures, graphics and the like to a digital format for displaying, editing, storing and outputting on computers. With advance of image technology, the scanner has become an indispensable device in computer systems used in homes and offices.
To accurately reproduce the pictures is one of the most important requirements of the scanner. As the scanning quality improves, the scanning resolution enhances, and scanning time also increases. This, to scan a great amount of documents taking a lot of time, becomes a problem to users.
In the past, the most effective approach to increase scanning speed is to increase the diaphragm of the lens, but the depth of field decreases when the diaphragm increases. The scanning position of the film scan in the scanning system and the Auto Document Feeder system will be different from the original correct scanning position, and the focal distance alters. This causes dropping of the Modulation Transfer Function (MTF), and affects the scanning quality.
Hence how to provide fast scanning speed without sacrificing the scanning quality has been a goal actively pursued in the industry.